JP2024515949A - Gel polymer electrolyte composition with shortened crosslinking time, secondary battery containing the same, and method for producing the secondary battery - Google Patents

Abstract

The present invention relates to a gel polymer electrolyte composition, a secondary battery including the same, and a method for manufacturing the secondary battery, and has the advantage of improving process efficiency by shortening the curing time of the gel polymer electrolyte while preventing electrolyte leakage.

Description

This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0038945, filed March 29, 2022, and Korean Patent Application No. 10-2022-0183228, filed December 23, 2022, and all contents disclosed in the documents of said Korean patent application are incorporated herein by reference.

The present invention relates to a gel polymer electrolyte composition with a shortened crosslinking time, a secondary battery containing the same, and a method for producing the secondary battery.

In recent years, secondary batteries, which can be charged and discharged, have been widely used as an energy source for wireless mobile devices. Secondary batteries are also attracting attention as an energy source for electric vehicles and hybrid electric vehicles, which have been proposed as a solution to address air pollution caused by existing gasoline and diesel vehicles that use fossil fuels. Therefore, the types of applications that use secondary batteries are becoming increasingly diverse due to the advantages of secondary batteries, and it is expected that secondary batteries will be applied to many more fields and products in the future.

A secondary battery has a structure in which an electrode assembly is built into a battery case together with an electrolyte, and the electrode assembly is sufficiently impregnated and wetted with the electrolyte to exhibit electrical performance. However, electrolyte leakage can occur during charging and discharging, which can cause battery cell failure and even fire.

Gel polymer electrolytes are being researched as a method to prevent electrolyte leakage. However, gel polymer electrolytes require a cross-linking process after the electrolyte is injected into the battery. This means that cross-linking the electrolyte takes a lot of time, which reduces the efficiency of the process and increases the unit production cost.

Therefore, there is a need for a technology that can reduce the curing time due to the cross-linking reaction within the electrolyte while introducing a gel polymer electrolyte to prevent electrolyte leakage.

The present invention was devised to solve the above problems, and aims to provide a gel polymer electrolyte composition that can significantly shorten the curing time compared to existing compositions, and a secondary battery containing the same.

The present invention provides a composition for a gel polymer electrolyte. In one embodiment, the composition for a gel polymer electrolyte according to the present invention includes an oligomer represented by the following chemical formula 1, a reaction additive including a phosphate-based compound, a polymerization initiator, a non-aqueous solvent, and a lithium salt.

In the above chemical formula 1, R is hydrogen or an alkylene having 1 to 5 carbon atoms substituted with an alkyl group having 1 to 5 carbon atoms, and m is an integer from 1 to 50.

In one embodiment, the gel polymer electrolyte composition has a curing time in the range of 10 to 50 minutes under heat treatment conditions of 55°C to 80°C.

In a specific embodiment, the content of the oligomer is in the range of 0.1 parts by weight to 30 parts by weight per 100 parts by weight of the total gel polymer electrolyte composition.

In another embodiment, the reaction additive is represented by the following chemical formula 2:

In the above formula 2, R ₁ , R ₂ and R ₃ are each independently hydrogen or an alkylene having 1 to 3 carbon atoms. When at least one of R ₁ , R ₂ and R ₃ is an alkylene having 1 to 3 carbon atoms, R ₄ , R ₅ and R ₆ are each independently a unit containing an acrylate group, a methacrylate group or a vinyl group.

In a specific embodiment, the reaction additive is represented by one or more of the following chemical formulas a to d.

In one embodiment, the content of the reaction additive is in the range of 0.01 parts by weight to 10 parts by weight per 100 parts by weight of the total gel polymer electrolyte composition.

The present invention also provides a method for manufacturing a lithium secondary battery by applying the above-mentioned gel polymer electrolyte composition. In one embodiment, the method for manufacturing a lithium secondary battery according to the present invention includes a step of injecting the gel polymer electrolyte composition according to claim 1 into a battery case in a state where an electrode assembly including a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode is housed in the battery case.

In one embodiment, the method for producing the lithium secondary battery further includes a step of performing thermal crosslinking for 10 to 50 minutes after the step of injecting the gel polymer electrolyte composition into the battery case.

In a specific embodiment, the thermal crosslinking step is carried out at a temperature in the range of 55°C to 80°C.

In another embodiment, the manufacturing method according to the present invention further includes a wetting step in which the gel polymer electrolyte composition is injected into the battery case and the thermal crosslinking step are performed while waiting for 1 minute to 30 hours.

In another embodiment, the manufacturing method according to the present invention further includes one or more of an activation step and a degassing step after the step of thermal crosslinking.

The present invention also provides a secondary battery manufactured by the above-mentioned method. In one embodiment, the lithium secondary battery according to the present invention includes an electrode assembly including a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode, a battery case that houses and seals the electrode assembly, and a gel polymer electrolyte composition injected into the battery case that houses the electrode assembly. The gel polymer electrolyte composition is as described above.

In a specific embodiment, the lithium secondary battery is a pouch-type battery.

The present invention can increase the efficiency of the manufacturing process for secondary batteries using thermally crosslinked gel polymer electrolytes, and improve the quality of the manufactured products.

1 is a schematic diagram illustrating a leakage evaluation process for a pouch-type secondary battery according to an embodiment of the present invention;

The present invention will be described in detail below. Before that, the terms and words used in this specification and claims should not be interpreted as being limited to their general or dictionary meanings, but should be interpreted as meanings and concepts that match the technical ideas of the present invention, based on the principle that the inventor can appropriately define the concept of the term in order to best describe his/her invention.

The present invention provides a composition for a gel polymer electrolyte. In one embodiment, the composition for a gel polymer electrolyte according to the present invention includes an oligomer, a reaction additive including a phosphate-based compound, a polymerization initiator, a non-aqueous solvent, and a lithium salt.

The present invention significantly increases the gelation rate of the electrolyte by adding a reactive additive that promotes the crosslinking reaction of the oligomer.

As one example, the oligomer may be a PPC (polypropylene carbonate) series oligomer. In one embodiment, the oligomer is represented by the following chemical formula 1:

In the above chemical formula 1, R is hydrogen or an alkylene having 1 to 5 carbon atoms substituted with an alkyl group having 1 to 5 carbon atoms, and m is an integer from 1 to 50.

Specifically, R is an alkylene having 1 to 3 carbon atoms, and more specifically, an alkylene having 2 carbon atoms substituted with a methyl group. The m is an integer from 1 to 10, an integer from 2 to 5, an integer from 2 to 3, or 2.

In one embodiment, the content of the oligomer in the present invention is in the range of 0.1 parts by weight to 30 parts by weight, based on 100 parts by weight of the total composition for gel polymer electrolyte. More specifically, the content of the oligomer is in the range of 1 part by weight to 10 parts by weight, 2 parts by weight to 8 parts by weight, or 3 parts by weight to 5 parts by weight. The content of the oligomer is in a range that prevents leakage of the electrolyte when applied to a secondary battery, while not degrading the performance of the secondary battery.

The curing temperature of the gel polymer electrolyte composition may vary depending on the type of polymerization initiator. In one embodiment, the crosslinking reaction of the gel polymer electrolyte composition proceeds under heat treatment conditions of 55°C to 80°C, 60°C to 75°C, or 68°C to 75°C, in which case the curing time is in the range of 10 minutes to 50 minutes, 10 minutes to 40 minutes, or 20 minutes to 40 minutes. The use of the reaction additive in the gel polymer electrolyte composition reduces the curing time by 25% or more compared to conventional methods.

In one embodiment, the reaction additive is represented by the following chemical formula 2:

In the above formula 2, R ₁ , R ₂ and R ₃ are each independently hydrogen or an alkylene having 1 to 3 carbon atoms, and when at least one of R ₁ , R ₂ and R ₃ is an alkylene having 1 to 3 carbon atoms, R ₄ , R ₅ and R ₆ are each independently a unit including an acrylate group, a methacrylate group or a vinyl group.

In the above description of Chemical Formula 2, when any one of R ₁ , R ₂ and R ₃ is hydrogen, it is interpreted that there is no substituent connected thereto.

In Formula 2, when any one or more of R ₁ , R ₂ and R ₃ has 4 or more carbon atoms, side reactions become significant, and thus performance degradation may occur when the compound is applied to a secondary battery.

In a specific embodiment, in the above Chemical Formula 2, R ₁ , R ₂ and R ₃ are each independently hydrogen or an alkylene having 1 to 2 carbon atoms, and when any one or more of R ₁ , R ₂ and R ₃ are an alkylene having 1 to 2 carbon atoms, R ₄ , R ₅ and R ₆ are each independently an acrylate group or a methacrylate group.

In a more specific embodiment, in the above formula 2, R ₁ , R ₂ and R ₃ are each independently an alkylene having 1 to 2 carbon atoms, and R ₄ , R ₅ and R ₆ are each independently an acrylate group or a methacrylate group.

In a more specific embodiment, in the above formula 2, R ₁ and R ₂ are alkylene having 1 to 2 carbon atoms, R ₃ is hydrogen, and R ₄ and R ₅ are each independently an acrylate group or a methacrylate group.

For example, the reaction additive is represented by one or more of the following chemical formulas a to d.

In the present invention, the content of the reactive additive is in the range of 0.01 parts by weight to 10 parts by weight based on 100 parts by weight of the total composition for gel polymer electrolyte. Specifically, the content of the reactive additive is in the range of 0.1 parts by weight to 10 parts by weight, 0.01 parts by weight to 5 parts by weight, 0.2 parts by weight to 5 parts by weight, or 0.5 parts by weight to 2 parts by weight. The content of such reactive additive is in a range that can sufficiently reduce the curing speed while minimizing the input amount.

The present invention also provides a method for manufacturing a lithium secondary battery to which the above-mentioned gel polymer electrolyte is applied. In one embodiment, the method for manufacturing a lithium secondary battery according to the present invention includes a step of injecting a composition for a gel polymer electrolyte into a battery case while an electrode assembly including a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode is housed in the battery case.

In the present invention, the above-mentioned gel polymer electrolyte composition is injected into a battery case containing an electrode assembly to manufacture a secondary battery. Then, a process of gelling the gel polymer electrolyte composition by heat treatment is performed. Specifically, the present invention includes a step of performing thermal crosslinking for 10 to 50 minutes after the step of injecting the gel polymer electrolyte composition into the battery case. The step of performing thermal crosslinking is a process of inducing a crosslinking reaction of the injected gel polymer electrolyte to harden it. The hardening time is in the range of 10 to 50 minutes, 10 to 40 minutes, or 20 to 40 minutes. The present invention has the effect of reducing the hardening time by 25% or more compared to the conventional method.

The temperature of the heat treatment for the thermal crosslinking step may vary depending on the type of polymerization initiator added. In the present invention, for example, a reactive additive represented by the above-mentioned Chemical Formula 2 may be used. In this case, the thermal crosslinking step may be performed at a temperature range of 55°C to 80°C, 60°C to 75°C, or 68°C to 75°C.

In another embodiment, the present invention includes a wetting step in which a waiting time of 1 minute to 30 hours is performed between the step of injecting the gel polymer electrolyte composition into the battery case and the step of performing thermal crosslinking.

In another embodiment, the present invention includes one or more of an activation step and a degassing step after the thermal crosslinking step.

The present invention also provides a secondary battery manufactured by the above-mentioned manufacturing method. In one embodiment, the secondary battery according to the present invention includes an electrode assembly including a positive electrode, one negative electrode, and a separator disposed between the positive electrode and the negative electrode, a battery case that houses and seals the electrode assembly, and a gel polymer electrolyte composition injected into the battery case that houses the electrode assembly. The gel polymer electrolyte composition is as described above.

Depending on the method of stacking the electrode assemblies, they can be classified into a wound jelly roll type and a stack type in which the electrodes are stacked sequentially. Depending on the shape of the battery case, secondary batteries can be classified into cylindrical batteries and prismatic batteries in which the electrode assembly is housed in a cylindrical or prismatic metal can, and pouch batteries in which the electrode assembly is housed in a pouch case of an aluminum laminate sheet. The secondary battery of the present invention can be a cylindrical, prismatic, or pouch type secondary battery, and is preferably a pouch type secondary battery.

Meanwhile, the case may be made of a laminate sheet including a metal layer and a resin layer. Specifically, the laminate sheet may be an aluminum laminate sheet. The battery case of the laminate sheet may include a lower case having a recessed storage section and an outer shell extending from the storage section, and an upper case joined to the lower case by thermal fusion.

The components of the secondary battery of the present invention are described below.

The positive electrode, which is one of the components of a secondary battery, has a structure in which a positive electrode active material layer is laminated on one or both sides of a positive electrode current collector. In one example, the positive electrode active material layer includes a positive electrode active material, a conductive material, a binder polymer, etc., and may further include a positive electrode additive commonly used in the industry as necessary.

The positive electrode active materials may be lithium-containing oxides, and may be the same or different. As the lithium-containing oxide, a lithium-containing transition metal oxide may be used.

For example, the lithium-containing transition metal oxide is Li _x CoO ₂ (0.5<x<1.3), Li _x NiO ₂ (0.5<x<1.3), Li _x MnO ₂ (0.5<x<1.3), Li _x Mn ₂ O ₄ (0.5<x<1.3), Li _x (Ni _a Co _b Mn _c ) O ₂ (0.5<x<1.3, 0<a<1, 0<b<1, 0<c<1, a+b+c=1), Li _x Ni _1-y Co _y O ₂ (0.5<x<1.3, 0<y<1), Li _x Co _1-y Mn _y O ₂ (0.5<x<1.3, 0≦y<1), Li _x Ni _1-y The compound may be any one selected from the group consisting of Mn _y O ₂ (0.5<x<1.3, 0≦y<1), Li _x (Ni _a Co _b Mn _c ) O ₄ (0.5<x<1.3, 0<a<2, 0<b<2, 0<c<2, a+b+c=2), Li _x Mn _2- z Ni _z O ₄ (0.5<x<1.3, 0<z<2), Li _x Mn _2-z Co _z O ₄ (0.5<x<1.3, 0<z<2), Li _x CoPO ₄ (0.5<x<1.3), and Li _x FePO ₄ (0.5<x<1.3), or a mixture of two or more of these. The lithium-containing transition metal oxide may be coated with a metal such as aluminum (Al) or a metal oxide. In addition to the lithium-containing transition metal oxide, one or more of sulfides, selenides, and halides may be used.

The positive electrode active material can be contained in the positive electrode active material layer in a range of 94.0% to 98.5% by weight. When the content of the positive electrode active material satisfies the above range, it is advantageous in terms of producing a high-capacity battery and imparting sufficient positive electrode conductivity and adhesive strength between electrode materials.

The current collector used in the positive electrode is a highly conductive metal to which the positive electrode active material slurry can easily adhere, and any metal that is non-reactive within the voltage range of the electrochemical device can be used. Specific, non-limiting examples of the current collector for the positive electrode include foils made of aluminum, nickel, or a combination thereof. The positive electrode active material layer further includes a conductive material.

Carbon-based conductive materials are often used as the conductive material, and include spherical (sphere type) and linear (needle type) carbon-based conductive materials. The spherical carbon-based conductive material fills the pores, which are the empty spaces between the active material particles, when mixed with a binder, improving the physical contact between the active materials, reducing the interfacial resistance, and improving the adhesive strength between the lower positive electrode active material and the current collector.

The conductive material may be contained in the positive electrode active material layer in an amount ranging from 0.5% to 5% by weight. When the content of the conductive material satisfies the above range, it provides sufficient conductivity to the positive electrode and has the effect of reducing the interfacial resistance between the electrode collector and the active material.

The binder polymer may be any binder commonly used in the art without any restrictions. For example, the binder may be a water-insoluble polymer that is soluble in organic solvents and insoluble in water, or a water-soluble polymer that is insoluble in organic solvents and soluble in water. The water-insoluble polymer may be one or more selected from the group including polyvinylidene fluoride (PVDF), polyvinylidene chloride (PVDC), polyacrylonitrile (PAN), polypropylene oxide (PPO), polyethylene oxide-propylene oxide copolymer (PEO-PPO), polytetrafluoroethylene (PTFE), polyimide (PI), polyetherimide (PEI), styrene butadiene rubber (SBR), polyacrylate, and derivatives thereof.

The water-soluble polymer may be one or more selected from the group including various cellulose derivatives such as carboxymethylcellulose (CMC), methylcellulose (MC), cellulose acetate phthalate (CAP), hydroxypropylmethylcellulose (HPMC), and hydroxypropylmethylcellulose phthalate (HPMCP).

The content of the binder polymer is proportional to the content of the conductive material contained in the upper and lower positive electrode active material layers. This is because it provides adhesive strength to the conductive material, which has a relatively small particle size compared to the active material, and because an increase in the conductive material content requires more binder polymer, whereas a decrease in the conductive material content requires less binder polymer to be used.

The negative electrode has a structure in which a negative electrode active material layer is laminated on one or both sides of a negative electrode current collector. In one example, the negative electrode active material layer includes a negative electrode active material, a conductive material, a binder polymer, etc., and may further include a negative electrode additive commonly used in the industry as necessary.

The negative electrode active material may include a carbon material, lithium metal, silicon, tin, or the like. When a carbon material is used as the negative electrode active material, both low crystalline carbon and high crystalline carbon may be used. Typical low-crystalline carbons are soft carbon and hard carbon, and typical high-crystalline carbons are natural graphite, kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, mesocarbon microbeads, mesophase pitches, and petroleum or coal tar pitch derived cokes and other high-temperature fired carbons.

Non-limiting examples of the current collector used in the negative electrode include foils made of copper, gold, nickel, or copper alloys, or combinations thereof. The current collector can also be used by laminating a substrate made of the above materials.

The negative electrode may also include conductive materials and binders commonly used in the field.

The separator may be any porous substrate used in lithium secondary batteries, for example, a polyolefin-based porous membrane or nonwoven fabric, but is not limited thereto.

Examples of the polyolefin-based porous membrane include membranes formed from polyolefin-based polymers such as polyethylene (such as high density polyethylene, linear low density polyethylene, low density polyethylene, and ultra-high molecular weight polyethylene), polypropylene, polybutylene, and polypentene, either alone or as a mixture of these polymers.

In addition to polyolefin-based nonwoven fabrics, the nonwoven fabrics include, for example, polyethylene terephthalate, polybutylene terephthalate, polyester, polyacetal, polyamide, polycarbonate, polyimide, Examples of nonwoven fabrics include polyetheretherketone, polyethersulfone, polyphenyleneoxide, polyphenylenesulfide, and polyethylenenaphthalene, each of which is used alone or in combination. The structure of the nonwoven fabric may be a spunbonded or meltblown nonwoven fabric made of long fibers.

The thickness of the porous substrate is not particularly limited, but may be 5 μm to 50 μm, and the size and porosity of the pores present in the porous substrate are also not particularly limited, but may be 0.01 μm to 50 μm and 10% to 95%, respectively.

Meanwhile, in order to improve the mechanical strength of the separator made of the porous substrate and to prevent short circuits between the positive and negative electrodes, a porous coating layer containing inorganic particles and a binder polymer may be further included on at least one surface of the porous substrate.

The electrolyte may include an organic solvent and an electrolyte salt, and the electrolyte salt may be a lithium salt. The lithium salt may be any lithium salt that is commonly used in non-aqueous electrolytes for lithium secondary batteries, without any limitations. For example, it contains Li ⁺ as a cation and F- ^{, Cl-} , ^Br- , ^I- , ^NO3- , N(CN) ^2- , ^BF4- , ^ClO4- , ^AlO4- _, ^AlCl4- , ^PF6- , ^SbF6- _, ^AsF6- , ^BF2C2O4- , ^BC4O8- , ( _CF3 ) ^2PF4- _{, (} ^{CF3 ) 3PF3-} _{, ( CF3} ⁾ _4PF2- ^, (CF3) _5PF- ^, ( _CF3 ⁾ _{6P- , CF3SO3- , C4F9SO3- , CF3CF2SO3-} , ( _CF3SO2 ) _2N- , ( _FSO2 ) ^2N- _, ^CF3CF2 ( _{CF3 ) 2CO-} ^, _{( CF3SO2 ) 2CH-} ^, ( _SF5 ) _3C- ^{, (} _CF3SO2 ⁾ _3C- , _{CF3 ( CF2} ) _{7SO3- , CF3CO2-} ^, _{CH3CO2- ,} ^SCN- , _and ( _CF3CF2SO2 ^{) 2N-} _.

As the organic solvent contained in the electrolyte described above, those generally used in electrolytes for secondary batteries can be used without any restrictions. For example, ethers, esters, amides, linear carbonates, cyclic carbonates, etc. can be used alone or in combination of two or more. Among them, representative carbonate compounds include cyclic carbonates, linear carbonates, and mixtures thereof.

Specific examples of the cyclic carbonate compounds include any one or mixtures of two or more selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, vinylene carbonate, vinylethylene carbonate, and halides thereof. Examples of these halides include, but are not limited to, fluoroethylene carbonate (FEC).

Specific examples of the linear carbonate compound include, but are not limited to, any one selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethyl methyl carbonate (EMC), methyl propyl carbonate, and ethyl propyl carbonate, or a mixture of two or more of these.

In particular, among the above carbonate-based organic solvents, the cyclic carbonates ethylene carbonate and propylene carbonate are high-viscosity organic solvents with high dielectric constants that can better dissociate the lithium salt in the electrolyte. By mixing such cyclic carbonates with linear carbonates with low viscosity and low dielectric constants such as dimethyl carbonate and diethyl carbonate in an appropriate ratio, an electrolyte with higher electrical conductivity can be produced.

As the ether of the organic solvents, any one selected from the group consisting of dimethyl ether, diethyl ether, dipropyl ether, methyl ethyl ether, methyl propyl ether, and ethyl propyl ether, or a mixture of two or more of these, can be used, but is not limited thereto.

The ester of the organic solvent may be any one selected from the group consisting of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone, and ε-caprolactone, or a mixture of two or more of these, but is not limited thereto.

The electrode assembly may be of a lamination/stack type in which unit cells with a separator interposed therebetween are stacked, or a stack/folding type in which unit cells are wound up with a separator sheet.

The electrode assembly is manufactured by applying an electrode active material to the positive and negative collectors to form a composite layer, manufacturing the positive and negative electrodes with pinholes in the electrode tab and electrode plate using a notching device, and bonding the positive and negative electrodes to a separator that does not contain pinholes. The type of the separator is not limited, but may be an organic/inorganic composite porous SRS (Safety-Reinforcing Separators) separator.

Specifically, the SRS separator is manufactured by using inorganic particles and a binder polymer as active layer components on a polyolefin-based separator substrate, and has a uniform pore structure formed by the pore structure contained in the separator substrate itself and the interstitial volume between the inorganic particles, which are active layer components. When such an organic/inorganic composite porous separator is used, it has an advantage that the increase in the thickness of the battery due to swelling during the formation process can be suppressed compared to the use of a general separator, and when a polymer that can be gelled when impregnated with a liquid electrolyte is used as the binder polymer component, it can be used simultaneously as an electrolyte. In addition, the organic/inorganic composite porous separator can exhibit excellent adhesive properties by adjusting the content of the inorganic particles and binder polymer, which are active layer components in the separator, and therefore has the characteristic that the battery assembly process can be easily performed.

The present invention will be described in more detail below with reference to examples. Since the present invention can be modified in various ways and can have various embodiments, specific examples are illustrated and described in detail in the text. However, this is not intended to limit the present invention to the specific disclosed form, and should be understood as including all modifications, equivalents, or alternatives falling within the spirit and technical scope of the present invention.

Example 1
_LiPF6 was dissolved as a lithium salt at a concentration of 1M in a solvent in which ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed at a volume ratio of 3:7, and additives were added in amounts based on the total weight of the gel polymer electrolyte as shown in Table 1 below to prepare gel polymer electrolyte compositions.

Specifically, the oligomer is added in an amount of 4% by weight, and the structural formula of the oligomer is as shown in Chemical Formula 1, where R is an alkylene having 2 carbon atoms substituted with a methyl group, and m is an integer ranging from 2 to 3.

The reactive additive is added at a content of 1% by weight, and the structural formula of the reactive additive is shown in chemical formula a below.

As a polymerization initiator, FUJIFILM WAKO's V-59 product, an azo-based thermal initiator, was used at a content of 1% by weight.

_{LiNi0.5Mn1.5O4} having a particle size of _{5 μm} was prepared as a positive electrode active material, and polyvinylidene fluoride as a carbon-based conductive agent and binder was mixed with N-methylpyrrolidone (NMP) in a weight ratio of 94:3:3 to form a slurry, which was cast on an aluminum sheet, dried in a vacuum oven at 120° C., and then rolled to manufacture a positive electrode.

Separately, a negative electrode active material was prepared by mixing artificial graphite and silicon oxide ( _SiO2 ) in a weight ratio of 9:1. 97 parts by weight of the negative electrode active material and 3 parts by weight of styrene-butadiene rubber (SBR) were mixed with water to form a slurry, which was then cast on a copper sheet, dried in a vacuum oven at 130°C, and rolled to produce a negative electrode.

The positive and negative electrodes obtained above were sandwiched between 18 μm polypropylene separators and inserted into a case, after which the gel polymer electrolyte composition was injected. After that, a pouch-type lithium secondary battery was manufactured after 30 minutes of curing at 70°C.

<Examples 2 to 4>
A gel polymer electrolyte composition was prepared in the same manner as in Example 1, except that the reactive additive was added in an amount of 1 wt % and the structural formula of the reactive additive was the following chemical formulas b to d, respectively.

A lithium secondary battery was manufactured using the gel polymer electrolyte composition produced in the same manner as in Example 1.

<Comparative Example 1>
An electrolyte composition was prepared by dissolving LiPF ₆ as a lithium salt at a concentration of 1M in a solvent in which ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed in a volume ratio of 3:7.

_{LiNi0.5Mn1.5O4} having a particle size of _{5 μm} was prepared as a positive electrode active material, and polyvinylidene fluoride as a carbon-based conductive agent and binder was mixed with N-methylpyrrolidone (NMP) in a weight ratio of 94:3:3 to form a slurry, which was cast on an aluminum sheet, dried in a vacuum oven at 120° C., and then rolled to manufacture a positive electrode.

Separately, a negative electrode active material was prepared by mixing artificial graphite and silicon oxide ( _SiO2 ) in a weight ratio of 9:1. 97 parts by weight of the negative electrode active material and 3 parts by weight of styrene-butadiene rubber (SBR) were mixed with water to form a slurry, which was then cast on a copper sheet, dried in a vacuum oven at 130°C, and rolled to produce a negative electrode.

A separator made of 18 μm polypropylene was placed between the positive and negative electrodes obtained above, and the electrodes were inserted into a case, after which the electrolyte composition was injected to produce a pouch-type lithium secondary battery.

<Comparative Example 2>
_LiPF6 was dissolved as a lithium salt at a concentration of 1M in a solvent in which ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed at a volume ratio of 3:7, and additives were added in amounts based on the total weight of the gel polymer electrolyte as shown in Table 1 below to prepare gel polymer electrolyte compositions.

A lithium secondary battery was manufactured using the gel polymer electrolyte composition produced in the same manner as in Example 1, but the curing time was set to 30 minutes.

<Comparative Example 3>
_LiPF6 was dissolved as a lithium salt at a concentration of 1M in a solvent in which ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed at a volume ratio of 3:7, and additives were added in amounts based on the total weight of the gel polymer electrolyte as shown in Table 1 below to prepare gel polymer electrolyte compositions.

A lithium secondary battery was manufactured using the gel polymer electrolyte composition produced in the same manner as in Example 1, but the curing time was set to 100 minutes.

<Comparative Example 4>
_LiPF6 was dissolved as a lithium salt at a concentration of 1M in a solvent in which ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed at a volume ratio of 3:7, and additives were added in amounts based on the total weight of the gel polymer electrolyte as shown in Table 1 below to prepare gel polymer electrolyte compositions.

A lithium secondary battery was manufactured using the gel polymer electrolyte composition produced in the same manner as in Example 1, but the curing time was set to 300 minutes.

<Comparative Example 5>
_LiPF6 was dissolved as a lithium salt at a concentration of 1M in a solvent in which ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed at a volume ratio of 3:7, and additives were added in amounts based on the total weight of the gel polymer electrolyte as shown in Table 1 below to prepare gel polymer electrolyte compositions.

However, the compound represented by the following chemical formula 1a was used as the oligomer component.

A lithium secondary battery was manufactured using the gel polymer electrolyte composition produced in the same manner as in Example 1, but the curing time was set to 30 minutes.

<Experimental example: Evaluation of the presence or absence of leakage>
The presence or absence of electrolyte leakage was evaluated for each of the secondary batteries manufactured in Examples 1 to 4 and Comparative Examples 1 to 3. Each secondary battery was a large cell of 100 Ah class.

The evaluation process is illustrated in FIG. 1. Referring to FIG. 1, each pouch-type secondary battery 100 is a large battery cell of 100 Ah class. The pouch-type secondary battery 100 has a structure in which an electrode assembly is housed in a pouch-type case. The pouch-type case is used as a reference, and a sealing area 120 is formed by heat sealing four sides surrounding the electrode assembly housing area 110, and electrode terminals 130 are led out to both sides. One side of the lower end of each pouch-type secondary battery 100 was cut open by about d (d=25 cm), tilted by an inclination angle θ (θ=5°), and stored at room temperature for one week. Thereafter, the amount of electrolyte leakage from each pouch-type secondary battery 100 was measured.

If the amount of electrolyte injected decreased by 3% or more by weight compared to the initial amount injected, it was determined that electrolyte leakage had occurred. The evaluation results are shown in Table 2 below.

With reference to Table 2, in Examples 1 to 4, no electrolyte leakage was observed even with a curing time of 30 minutes. In contrast, in Comparative Example 1, the electrolyte did not gel, and therefore leakage was observed. With reference to Comparative Examples 2 and 3, it can be seen that when the reactive additive according to the present invention is not added, electrolyte leakage is observed with a curing time of 30 minutes or 100 minutes. With reference to Comparative Example 4, it can be seen that when the reactive additive is not added, no leakage is observed with a curing time of 300 minutes. And in Comparative Example 5, electrolyte leakage was observed. In Comparative Example 5, a compound represented by chemical formula 1a was used as the oligomer component, and it was confirmed that sufficient curing did not proceed through 100 minutes of curing.

100: pouch-type secondary battery 110: electrode assembly housing area 120: sealing area 130: terminal

Claims (13)

An oligomer represented by the following chemical formula 1:
a reactive additive comprising a phosphate-based compound;
A polymerization initiator,
a non-aqueous solvent; and a lithium salt;

In the above Chemical Formula 1,
R is hydrogen or an alkylene having 1 to 5 carbon atoms substituted with an alkyl group having 1 to 5 carbon atoms;
A composition for a gel polymer electrolyte, wherein m is an integer of 1 to 50. The gel polymer electrolyte composition according to claim 1, wherein the curing time of the gel polymer electrolyte composition is in the range of 10 to 50 minutes under heat treatment conditions of 55°C to 80°C. The gel polymer electrolyte composition according to claim 1, wherein the content of the oligomer is in the range of 0.1 parts by weight to 30 parts by weight per 100 parts by weight of the total gel polymer electrolyte composition. The reaction additive is represented by the following chemical formula 2:
In the above Chemical Formula 2,
R ₁ , R ₂ and R ₃ each independently represent hydrogen or alkylene having 1 to 3 carbon atoms;
The composition for gel polymer electrolyte according to claim 1, wherein when any one or more of R ₁ , R ₂ and R ₃ is an alkylene having 1 to 3 carbon atoms, R ₄ , R ₅ and R ₆ are each independently a unit containing an acrylate group, a methacrylate group or a vinyl group. The composition for gel polymer electrolyte according to claim 1, wherein the reactive additive is represented by any one or more of the following chemical formulae a to d:
The gel polymer electrolyte composition according to claim 1, wherein the content of the reactive additive is in the range of 0.01 parts by weight to 10 parts by weight per 100 parts by weight of the total gel polymer electrolyte composition. In a state where an electrode assembly including a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode is housed in a battery case,
A method for producing a lithium secondary battery, comprising the step of injecting the gel polymer electrolyte composition according to claim 1 into a battery case. After the step of injecting the gel polymer electrolyte composition into the battery case,
The method for manufacturing a lithium secondary battery according to claim 7, further comprising the step of performing thermal cross-linking for a period ranging from 10 minutes to 50 minutes. The method for producing a lithium secondary battery according to claim 8, wherein the thermal cross-linking step is carried out at a temperature range of 55°C to 80°C. The method for producing a lithium secondary battery according to claim 8, further comprising a wetting step of waiting for 1 minute to 30 hours between the step of injecting the composition for the gel polymer electrolyte into the battery case and the step of performing thermal crosslinking. The method for producing a lithium secondary battery according to claim 8, further comprising at least one of an activation step and a degassing step after the step of performing thermal crosslinking. an electrode assembly including a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode;
A lithium secondary battery comprising: a battery case that houses and seals the electrode assembly; and the gel polymer electrolyte composition according to claim 1 injected into the battery case housing the electrode assembly. The lithium secondary battery according to claim 12, wherein the lithium secondary battery is a pouch-type battery.

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